(1) Recently, radio waves generated from electronic devices such as personal computers, mobile phones, flat panel displays such as liquid crystal displays and plasma displays, touch panels, car navigation systems, mobile information terminals, mobile game devices and the like cause malfunction and communication failure of other machines or electronic devices, which is a serious problem. In addition, it has been indicated that radio waves have a harmful effect on the human body. In order to prevent the so-called electromagnetic interference (hereinafter, referred to as the “EMI”), measures are taken by using various electromagnetic wave-shielding materials. However, light-transmitting electromagnetic wave-shielding laminate bodies are often used outdoors under severe conditions and cannot be practically used unless fulfilling various performance requirements other than the electromagnetic wave-shielding performance.
For example, there are the following problems. The car navigation systems used in vehicles, mobile phones, mobile information terminals, mobile game devices and the like need to be used in a high temperature and high humidity condition. Therefore, in the case where the layers are laminated with a usual adhesive, the adhesive itself becomes cloudy by hydrolysis, or water vapor enters an interface between the adhesive and the layers to be bonded and becomes cloudy. Therefore, the transparency and visibility cannot be obtained. Liquid crystal displays and plasma displays for advertisement, displays of vending machines and ticket machines, and the like used outdoors are yellowed or cause peeling to the laminate body thereof due to long-term deterioration by ultraviolet or rainwater. Therefore, the transparency and visibility are lowered. In addition, when the light-transmitting electromagnetic-shielding laminate is drilled or cut in order to be attached to various electronic devices, an end surface of the laminate body is peeled.
As an adhesive for lamination of a light-transmitting electromagnetic-shielding laminate, Japanese Laid-Open Patent Publications Nos. 2001-26758 and 2001-19925 describe adhesive compositions having an ethylene-vinyl acetate (EVA) copolymer adhesive composition or a copolymer of ethylene, vinyl acetate and/or a (meth)acrylate-based monomer as main components. These adhesive compositions all have inconveniences that the compositions become cloudy under a high temperature and high humidity condition and so the visibility cannot be obtained, peeling is caused to the laminate body due to rainwater, the adhesive force is weak and so an end surface of the laminate body is peeled at the time of drilling or cutting.
As an adhesive for a light-transmitting electromagnetic-shielding laminate, Japanese Laid-Open Patent Publication No. 2004-140283 describes a hotmelt-type adhesives of an ethylene-vinyl acetate (EVA) copolymer or an ethylene-acrylic acid ester copolymer. Such an adhesive has the following problems. In a high temperature and high humidity condition, the adhesive itself becomes cloudy, or water or moisture enters between the substrate and the adhesive and so condenses to become cloudy. As a result, the visibility is significantly lowered. In addition, because the adhesive force is insufficient, an end surface of the laminate body is peeled at the time of drilling or cutting.
As an adhesive for a light-transmitting electromagnetic-shielding laminate, Japanese Laid-Open Patent Publications Nos. 2006-319251 and 10-163673 describe acrylic-based, rubber-based, silicone-based, polyurethane-based, and polyester-based transparent tacky agents. Because such a tacky agent does not have a sufficient adhesive force, the following problems occur. In a high temperature and high humidity condition, water or moisture enters between the substrate and the tacky agent and so condenses to become cloudy. As a result, the visibility is significantly lowered. In addition, an end surface of the laminate body is peeled at the time of drilling or cutting.
As an adhesive for a light-transmitting electromagnetic-shielding laminate, Japanese Laid-Open Patent Publication No. 11-330778 describes an urethane-based adhesive. Although having a certain degree of adhesive force, the urethane-based adhesive becomes cloudy in a high temperature and high humidity condition, and so the visibility is significantly lowered. This publication does not disclose any detailed composition of the adhesive or any explanation or example of the processability of the adhesive.
(2) Recently, the development of wireless communication systems such as mobile phones, wireless LAN (Local Area Network), ITS (Intelligent Transport Systems) and the like has realized interactive large capacity communication. Such technologies are being rapidly spread in the daily life and industries. In ETC (Electronic Toll Collection) systems and AHS (Advanced Cruise-Assist Highway Systems) provided for the purpose of solving the traffic jam at the freeway toll gates or improving the convenience through the cashless system, DSRC (Dedicated Short-Range Communication) systems are used for performing radio wave communication between a roadside unit installed on the road and an onboard unit mounted on a vehicle. Such a system is expected to be used for payment at in gas stations, fast food stores, car parks and the like in addition to be used on the road.
Along with the spreading of these technologies, noise generation, line crossing, communication error, malfunction, information leakage and the like occur as social problems. In order to solve these problems, radio wave absorbers for absorbing unnecessary radio waves are installed. Conventional radio wave absorbers are non-light-transmitting or do not transmit sufficient light, and so are only usable in limited sites.
In airports, train stations, offices, hospitals and the like, a light-transmitting radio wave absorber, which is superb in radio wave absorbing performance and weather resistance and improves the indoor and outdoor radio wave environment, is required in order to prevent noise generation, line crossing, communication error, malfunction and information leakage without spoiling the scenic view or lighting. At the freeway tool gates, and cashiers of the gas stations, fast food stations, car parks and the like, communication failures such as line crossing, communication error, and the like need to be solved. In addition, at the toll gates, poor visibility involves a possibility of causing serious accidents such as minor collisions between vehicles. In the gas stations and car parks, poor visibility involves a possibility of causing serious accidents such as collisions between humans and vehicles. In these circumstances, a light-transmitting radio wave absorber which is superb in visibility in addition to radio wave absorbing performance and weather resistance is required.
However, light-transmitting radio wave absorbers are often used outdoors under severe conditions and cannot be practically used unless fulfilling various performance requirements. For example, there are the following problems. In the case where the layers are laminated with a usual adhesive, a radio wave absorber becomes cloudy in a high temperature and high humidity condition, and so the visibility cannot be obtained. In addition, the radio wave absorber is yellowed or causes peeling to the laminate body thereof due to long-term deterioration by ultraviolet or rainwater. Therefore, the transparency and visibility are lowered. Moreover, when the laminate body of the radio wave absorber is drilled or cut for installation, an end surface thereof is peeled.
As an adhesive for lamination of a light-transmitting radio wave absorber, Japanese Laid-Open Patent Publication No. 2003-324300 describes EVA (ethylene-vinyl acetate copolymer), PVB (polyvinylbutyral), urethane-based, and epoxy-based adhesives. These adhesives all have the inconveniences of becoming cloudy under a high temperature and high humidity condition or causing peeling to the laminate body due to rainwater. This publication also describes denatured polyethylene and denature polypropylene, but all these materials have problems in adhesive force, and so an end surface of the laminate body is peeled at the time of drilling or cutting by a jigsaw.
As an adhesive for a light-transmitting radio wave absorber, Japanese Laid-Open Patent Publications Nos. 2000-59068, 2000-174545, and 2005-85966 describe an acrylic-based tacky agent. However, in a high temperature and high humidity condition, water or moisture enters between the substrate and the tacky agent and so condenses to become cloudy. As a result, the visibility is significantly lowered. In addition, because such a tacky agent does not have a sufficient adhesive force, the problem that, for example, an end surface of the laminate body is peeled at the time of drilling or cutting by a jigsaw occurs.
As an adhesive for a light-transmitting radio wave absorber, Japanese Laid-Open Patent Publication No. 9-186486 describes a (meth)acrylic-based ultraviolet-curable adhesive. Such a usual (meth)acrylic-based ultraviolet-curable adhesive becomes cloudy in a high temperature and high humidity condition and so the visibility is lowered, and also has a weak adhesive force and so causes an end surface of the laminate body to be peeled at the time of drilling or cutting by a jigsaw. This publication does not disclose any detailed composition of the adhesive or any explanation or example of the processability of the adhesive.
(3) In today's society, a light-transmitting resin laminate material is used in various sites such as, for example, flat panel displays of liquid crystal display devices or plasma display devices; displays of touch panels, car navigation systems, mobile phones, mobile game devices and the like; optical storage mediums such as MOs (magneto-optic discs), DVDs (digital versatile discs), Blu-ray discs, and the like; optical materials such as polarizing films and lenses, etc.; construction materials such as carports, light-transmitting resin sound-proof walls, materials for windows with security equipment, and the like; and light-transmitting radio wave absorbing laminate bodies used to prevent communication errors of ETC (Electronic Toll Collection) systems and DSRC (Dedicated Short-range Communication) systems for performing radio wave communication between a roadside unit installed on the road and an onboard unit mounted on a vehicle. However, light-transmitting resin laminate bodies are often used outdoors under severe conditions and cannot be practically used unless fulfilling various performance requirements.
For example, there are the following problems. The car navigation systems used in vehicles, mobile phones, mobile game devices, DVDs, Blu-ray discs and the like need to be used in a high temperature and high humidity condition. Therefore, in the case where the layers are laminated with a usual adhesive, the adhesive itself becomes cloudy by hydrolysis, or water vapor enters an interface between the adhesive and the layers to be bonded and becomes cloudy. Therefore, the transparency and visibility cannot be obtained. Carports, light-transmitting sound-proof walls, materials for windows with security equipment, light-transmitting radio wave absorbing laminate bodies, and the like used outdoors are yellowed or cause peeling to the laminate body thereof due to long-term deterioration by ultraviolet or rainwater. Therefore, the visibility and functionality are lowered. In addition, an end surface of the laminate body is peeled at the time of drilling or cutting.
As an adhesive for an optical disc laminate body, Japanese Laid-Open Patent Publication No. 2000-186253 describes a photo-curable adhesive containing a radical polymerizable vinyl compound, a specific (meth)acrylate compound and a radical polymerization initiator. Japanese Laid-Open Patent Publication No. 2003-196884 describes an ultraviolet-curable adhesive composition containing a mono-functional (meth)acrylate including a branching alkoxyl group having a carbon number of 4 or greater and a photoinitiator. These adhesives all have problems of being hydrolyzed when immersed in warm water and so becoming cloudy to significantly lower the visibility, and having an insufficient adhesive force and so causing an end surface of the laminate body to be peeled at the time of drilling or cutting by a jigsaw. For these problems, these adhesives cannot be used as an adhesive for lamination of an light-transmitting resin laminate body.
As an adhesive for an optical element laminate body, PCT National Phase Japanese Laid-Open Patent Publication No. 2006-522856 describes a pressure-sensitive adhesive composition containing (meth)acrylamide and an alkoxysilane compound. Although the high temperature and high humidity resistance is improved, the adhesive does not have a sufficient adhesive force because of being the pressure-sensitive type, and so has a problem that an end surface of the laminate body is peeled at the time of processing. For these reasons, this adhesive cannot be used as an adhesive for lamination of an light-transmitting resin laminate body.
As an adhesive for an optical disc laminate body, Japanese Laid-Open Patent Publication No. 2006-104446 describes an adhesive composition containing bisphenol-type epoxy (meth)acrylate, di(meth)acrylate, a photoinitiator and (meth)acrylate phosphate. Although the high temperature and high humidity resistance is improved, the adhesive does not have a sufficient adhesive force, and so an end surface of the laminate body is peeled at the time of processing. In addition, there is a problem that because bisphenol type epoxy (meth)acrylate is used, the adhesive itself is yellowed to spoil the external appearance when being used outdoors at a site exposed to ultraviolet.
As an adhesive for lamination of a transparent radio wave absorber, Japanese Laid-Open Patent Publication No. 2003-324300 describes EVA (ethylene-vinyl acetate copolymer), PVB (polyvinylbutyral), urethane-based, and epoxy-based adhesives. These adhesives all have the inconveniences of becoming cloudy under a high temperature and high humidity condition or causing peeling to the laminate body due to rainwater. This publication also describes denatured polyethylene and denature polypropylene, but all these materials have problems in adhesive force, and so an end surface of the laminate body is peeled at the time of drilling or cutting by a jigsaw.